Conventional mobile machines are known to include a power source, such as a diesel or gasoline powered engine, that is operatively connected through a drivetrain to traction devices for propulsion. To control the temperature of the engine and other components during operation, such machines may also include a liquid cooling system generally consisting of a pump fluidly connected through one or more conduits to circulate coolant through a power source coolant jacket and a heat exchanger. The heat exchanger may be associated with a cooling fan that provides a flow of air to draw heat from the exchanger, thereby providing more effective cooling. Other machine components, such as a transmission and torque converter fluid cooler, hydraulic system or brake fluid cooler, and engine oil cooler, may be fluidly connected to the same cooling system to control the temperature of fluids associated therewith. Thermal management during engine warm-up or under idle conditions is typically controlled by a thermostat connected to a by-pass conduit that restricts the flow of coolant from the system to the heat exchanger. However, other machine components connected to the system may continue to draw heat away from the power source.
At initial start-up and during idling, particularly in cold environmental conditions, the initial responsiveness and performance of the power source and other machine systems can suffer. More importantly, however, it is known that at low temperatures, even at room temperature, carbon deposits may begin to form on injectors, valves and other engine components. This can affect engine performance and efficiency, decrease operating life, increase servicing and operating costs, and increase machine downtime. Other systems may also suffer under cold conditions. For example, increased viscosity of the various fluids may result in lack of responsiveness. In particular, hydraulic systems may suffer from decreased inlet pressures which may result in cavitation damage, and lack of responsiveness. Transmissions may suffer from reduced lubrication of bearings and other components, slow shifting and movement of parts, again affecting performance and potentially leading to premature wear and damage to machine components.
To address the problems associated with cold start and idle conditions, it is known to provide an elevated idle that increases engine RPMs at low temperatures when the machine is not moving. More specifically, a temperature sensor is associated with the engine to provide a signal indicative of the engine coolant temperature, the signal being provided to a controller configured to increase engine idle speed, while in a parked or neutral operating condition, until a desired temperature is achieved. However, this strategy may not be sufficient to maintain the temperatures necessary to avoid the above problems, particularly those associated with carbon build-up, and may result in excess noise and lower fuel economy.
U.S. Pat. No. 7,267,633 to Hitch and Kluemper discloses selectively controlling the state of a fluid coupling in a motor vehicle powertrain during neutral idle operation of the engine to increase engine temperatures. The fluid coupling includes an output member that is selectively grounded through transmission clutches under specified enable conditions to impose an engine load for raising the engine operating temperature. The clutches are released to resume normal operation of the powertrain when the enable conditions are no longer met or an estimate of the fluid temperature of the coupling reaches or exceeds a predefined temperature. However, this strategy relies purely on increasing the load on the engine, which may increase noise and lower fuel economy. Moreover, the temperature controls that protect the fluid coupling from overheating may place limitations on the heating capacity of the system. That is, there may be conditions under which the desired engine temperature has not been attained, while the clutches have been disengaged because the temperature of the fluid coupling has exceeded the predefined temperature. In general, it would be desirable to improve the efficiency of such a system, increasing heating capacity and decreasing overall fuel consumption and noise.
The present disclosure is directed to overcoming one or more of the problems set forth above.